Eurocopter hybrid patent: A preview of X3 or X4?

Eurocopter_hyrbrid_zoom.JPGA US patent application (No. 20100065677)submitted by Eurocopter last March and published last week hints at some of the radical new concepts the top rotorcraft manufacturer as been tinkering with in its labs as part of what company CEO Lutz Bertling says is a drive to “extend the domain” of the helicopter.

It’s not clear whether the hybrid concept, which features a canard stabilizer and swept wings with dual pusher props for anti-torque and forward thrust, is related to ongoing X3 and X4 technology programs within the company.

X3 was briefly (and mistakenly) mentioned by Rolls-Royce at the 2009 Heli Expo show in relation to Rolls providing an RTM322 turboshaft engine for the project. Eurocopter has revealed that the X4 is being designed as an update of the Dauphin line of helicopters. Bertling said at this year’s Heli Expo that Eurocopter will perform first flights of two new or upgraded models in the third quarter of 2010, bringing both rotorcraft to the 2011 Heli-Expo show.

The design in the patent application, described as a “hybrid helicopter that is fast and has long range”, features elements that would make a helicopter safer and quieter, but by my reading, not faster. Bertling has said safety and noise achievements will be hallmarks of the X4, particularly if the company is successful in getting a requested stimulus package from the French government this spring. “The company is prepared to take much higher risk in using new technologies if we get the aid,” Bertling told me at the 2010 Heli-Expo in Houston. 

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Design features that add to passenger comfort include getting rid of the “tail shake” effect caused by downward wake from the main rotor on a tail boom, and for which present day helicopters counter with active devices that are “expensive and heavy”, says Eurocopter in the application.

By placing the canard stablizer at the front of the aircraft, ahead of the rotor, Eurocopter says this hybrid does not have the traditional “attitude hump” phenomena that causes attitude disturbances during acceleration and deceleration events. 

Wing-mounted pusher propellers, which have variable pitch mechanisms, are driven through a fixed-ratio rotating shaft system from the main rotor and engine(s). 

Missing from the application is any mention of why this particular configuration would be faster than a traditional helicopter, which is hindered by the retreating blade stall and other issues at speeds beyond about 160kt (300km/h).   

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